1. Field of the Invention
The present invention relates to sheet metal tools that are not planar and are of the type used for cutting and abrading nonlinear surfaces and, specifically, to a method for chemically machining such tools to provide cutting teeth of unique and highly efficient shapes.
2. Description of the Prior Art
Over the millenia, cutting and filing instruments have been the tools of the trade in a wide range of occupations. From art to woodworking, ideas for tool uses crosspollinate between the various tool-using professions. For example, a hacksaw cuts metal, wood or bone, depending on the profession of the user. Each profession, however, may have its own particular demands for tools. For instance, a hacksaw cutting metal may require a blade with different specifications than the surgical version.
Toolmaking has improved and expanded over the years to meet these particular professional demands. Yet, there is a need for better performing cutting tools. Many prior art instruments are punched out of sheet metal. The sheet metal passes through a punch and die, a procedure that imparts holes in the metal. The edges of the holes are then bent to provide the necessary "set" to make the desired cutting edge profile, such as a tooth.
These state-of-the-art instruments lack a preferred degree of sharpness. This is partially the result of the cutting edges being formed by the ragged die cuts in the metal blank. More expensive instruments have ground edges, however, this grinding process is limited in both application and possible tooth arrangements because the grinding well or broach is required to enter and exit the tooth in a straight line. As a result, the available tooth patterns are relatively simple and linear.
Because of the high cost of tooling and grinding, attempts were made to manufacture sheet metal instruments by chemical etching. These endeavors resulted in end products that tended to do more rubbing than cutting, primarily due to the lack of side, frontal and/or top relief in the etched individual tooth patterns.
The method of toolmaking revealed in U.S. Pat. No. 5,100,506 is a major improvement in toolmaking. This patent discloses a method of chemically machining tools to provide sharp cutting teeth of unique and highly efficient shapes. The method works effectively to machine cutting edges on planar sheet metal objects, such as flat rasps, files and saw blades. The improvements were not specifically directed, however, toward sheet metal objects that are not planar.
The above prior art does not specifically address the problems of making cutting tools that are not planar. Such instruments perform a variety of functions, typically smoothing and cutting nonlinear surfaces. The prior art instruments with cutting edges on curved surfaces may use no teeth, for example, an acetabular reamer with punched holes for cutting edges. Each hole in the acetabular reamer is individually drilled, countersunk and set from the inside of the hemisphere. This produces an instrument that easily clogs and dulls. Therefore, new methods are needed to produce better cutting tools for curved surfaces.
Surgical procedures have been performed using tools since at least the neolithic era. Surgical instruments frequently evolve from the tools of other professions, like cutting blades and scissors common to both medicine and barbering. Other instruments derive from the saws, rasps, gouges and files from woodworking and metalworking.
Surgical procedures often involve cutting and filing tough tissue such as bone and cartilage. In hip implant surgery, both the head of the femur or the "ball" and acetabulum or cup shaped pelvic socket are removed and replaced with artificial counterparts. To attach the prosthetic head, a longitudinal cavity must be reamed down the femur to anchor the stem of the head using a T-handle femoral shaft reamer or broach. After replacing the head, the surgeon deepens the acetabulum by reaming or gouging until it accepts the acetabular prosthesis.
These prior art surgical instruments have several disadvantages. They often require extensive hand finishing to form the cutting edges. They dull quickly and are heavy. Dull cutting instruments roughly grind and scrape rather than cut the tissue. In surgery, smooth cutting reduces the risks of sepsis or infection. Dull instruments also require more force to remove the tissue from its location. For example, disposable scalpel blades with reusable handles are preferred over reusable scalpels. The cutting edge of a reusable scalpel dulls quickly, thereby requiring constant sharpening for efficient use. Since a surgical procedure cannot be interrupted to sharpen the cutting edge, many reusable scalpels are often needed. Heavy weight instruments generate heat and are fatiguing to use.
The prior art surgical instruments are reusable and therefore require designs for easy cleaning of tissue. This requirement hinders the design of more effective cutting surfaces. Reusable instruments are immediately cleaned and sterilized to prevent degradation of the instrument and prepare them for reuse. Tissue traps and lodges within complex cutting edges, thereby requiring hand cleaning to ensure adequate tissue removal. The instruments must first soak in germicidal detergent solutions which do not always effectively kill all infectious agents, thereby presenting a risk to the worker who cleans the instruments. Chlorine solutions such as bleach effectively kill infectious agents but degrade the metal in the instruments. Ultrasonic cleaning after hand cleaning helps remove much of the trapped tissue, however, the problems of infectious agents still exist. Sterilizing the equipment prior to cleaning is not recommended. The tissue degrades the metal. Further, sterilizing before cleaning hardens the tissue on the instrument making it difficult to remove.
Sharper and lighter surgical instruments are thus desirable. Sharper instruments cut tissue smoothly with less force rather than grinding or scraping it. Lighter instruments must be strong enough to withstand the forces placed on the instrument during surgery, such as reaming out the femur during hip replacement surgery. The lighter sheet metal cannot deform or break during punching and forming the cutting edges.
Chemically machined instruments from sheet metal use lighter sheet metal. The sheet metal is lighter, yet strong, resisting deformation and breakage. Chemically machined edges are sharper and require less hand finishing. Since thinner and lighter metals are used, the tools can be disposable.
It is an object of the invention to provide an improved chemical machining method for manufacturing cutting tools that are not planar which overcomes the previously mentioned shortcomings. Another object of the invention is to provide improved cutting tools for nonlinear surfaces.
Another object of the invention is to provide a greater array of cutting edges or tooth designs for such tools that cut materials more efficiently than the presently available designs.
Another object of the invention is to provide improved sheet metal cutting tools that are not planar and a method of manufacture that eliminates the necessity of grinding the cutting edges, the use of expensive dies and fixtures or extensive hand finishing of the instrument.
Another object of the invention is to provide effective and inexpensive cutting tools that are not planar for surgical use.